Effect of OH species in the oxynitride titanium formation during plasma-assisted thermochemical treatment

Abstract

Currently, the study of oxynitrides surfaces emerges as one of the most promising ways to obtain improvements in several properties of titanium and expand its applications. In this context, the plasma-assisted thermochemical technique has stood out due to its versatility and easy to control precisely the structure and composition of the compound layer. In this work, titanium samples were subjected to 40%H 2 –60%N 2 and 40%H 2 –45%N 2 –15%O 2 plasma treatment for surface modification where the effect of OH species in the oxynitride formation was investigated. Grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and X-ray induced photoelectron spectroscopy (XPS) were used for structural and chemical composition analyses. Also, optical emission spectroscopy (OES) was used in order to study the plasma chemistry. Results evidenced that the addition of H 2 , which consequently increases the concentration of OH species in the plasma, during the pre-treatment and treatment was important for the cleaning and reduction of native titanium oxides. XPS results showed that the titanium surface, which had 92% Ti O bond before treatment, was totally reduced, giving rise to Ti-N-O (56%) and Ti N (44%) bonds when nitrided. When oxygen was added to the atmosphere, the Ti N bond disappeared, giving rise to the Ti O bond (27%) and Ti-N-O bond (73%). The treatments were suitable for oxynitriding the titanium surface in a predominantly diffusive process with about 290 nm thickness. Material analysis allow us to describe the main mechanisms for oxynitride formation as well as correlate this phenomenology with some investigated plasma properties by OES analysis.